System and assemblies for hot water extraction to pre-heat fuel in a combined cycle power plant

ABSTRACT

A system and assemblies for a fuel supply system are provided. The system includes a water heater assembly configured to heat a flow of water by mixing progressively higher grade heated flows of at least one of steam and water from a multi-stage heat exchanger arrangement, a fuel inlet flow path configured to receive a flow of fuel, and a fuel heater including a first flow path coupled in flow communication with the fuel inlet flow path and a second flow path coupled in flow communication with the water heater assembly wherein the fuel heater is configured to transfer heat from the flow of water to the flow of fuel.

BACKGROUND OF THE INVENTION

This invention relates generally to power generation systems and, moreparticularly, to a system and assemblies for pre-heating fuel in acombined cycle power plant.

At least some known power generation systems include a multi-stage heatrecovery steam generator (HRSG) configured to generate progressivelylower grade steam from each successive stage in the exhaust of a gasturbine engine. Relatively high grade heat at a gas inlet to the HRSG iscapable of generating relatively high pressure steam in a high pressurestage or section of the HRSG. After heat is removed from the gas in thehigh pressure stage the gas is channeled to an intermediate pressurestage where the relatively cooler gas is only capable of generating arelatively lower pressure or intermediate pressure steam.

To reduce the fuel consumption in the gas turbine engine the fuel istypically preheated. The preheating of the fuel uses one or more waterflows from respective HRSG sections to heat the fuel in a multi-stagefuel heater. However, the amount of heat addition to the fuel using asingle stage or multistage fuel heater is limited.

BRIEF DESCRIPTION OF THE INVENTION

In one embodiment, a fuel supply system includes a water heater assemblyconfigured to heat a flow of water by mixing progressively higher gradeheated flows of at least one of steam and water from a multi-stage heatexchanger arrangement, a fuel inlet flow path configured to receive aflow of fuel, and a fuel heater including a first flow path coupled inflow communication with the fuel inlet flow path and a second flow pathcoupled in flow communication with the water heater assembly wherein thefuel heater is configured to transfer heat from the flow of water to theflow of fuel.

In another embodiment, a water heater assembly is configured to heat aflow of water by mixing progressively higher grade heated flows of atleast one of steam and water from a multi-stage heat exchangerarrangement. The water heater assembly includes an inlet configured toreceive a flow of condensate water from a relatively lower pressure heatexchanger positioned in the multi-stage heat exchanger arrangement and aflash tank mixing vessel that includes a plurality of inlet flow pathsand an outlet. The flash tank mixing vessel is configured to receive aflow of at least one of steam and water from a respective heat exchangerin the multi-stage heat exchanger arrangement coupled in flowcommunication to each of the plurality of inlet flow paths.

In yet another embodiment, a fuel heater assembly is configured to heata flow of water by mixing progressively higher grade heated flows of atleast one of steam and water from a multi-stage heat exchangerarrangement. The fuel heater assembly includes a water heater assemblythat includes a plurality of inlet flow paths configured to receive aflow of at least one of water and steam from respective heat exchangerspositioned in the multi-stage heat exchanger arrangement wherein therespective heat exchangers correspond to a plurality of different gradesof heat in the multi-stage heat exchanger arrangement. The water heaterassembly also includes an outlet configured to channel the heated flowof condensate from the water heater assembly. The fuel heater assemblyalso includes a fuel heater that includes a first flow path configuredto be coupled in flow communication with a flow of fuel, and a secondflow path configured to be coupled in flow communication with the outletwherein the fuel heater is configured to transfer heat from the flow ofwater to the flow of fuel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 show exemplary embodiments of the system and assembliesdescribed herein.

FIG. 1 is a schematic diagram of an exemplary combined cycle powergeneration system; and

FIG. 2 is a schematic diagram of the water heater assembly, shown inFIG. 1, in accordance with an exemplary embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description illustrates embodiments of theinvention by way of example and not by way of limitation. It iscontemplated that the invention has general application to improvingefficiency of combustion and power generation systems by usingprogressively higher grade heat to preheat a fuel flow to a combustor inindustrial, commercial, and residential applications. As used hereinhigh grade heat refers to heat at a relatively high temperature, lowgrade heat refers to heat at a relatively low temperature, andintermediate grade heat refers to heat at a temperature between that oflow and high grade heat.

As used herein, an element or step recited in the singular and proceededwith the word “a” or “an” should be understood as not excluding pluralelements or steps, unless such exclusion is explicitly recited.Furthermore, references to “one embodiment” of the present invention arenot intended to be interpreted as excluding the existence of additionalembodiments that also incorporate the recited features.

FIG. 1 is a schematic diagram of an exemplary combined cycle powergeneration system 5. Power generation system includes a gas turbineengine assembly 7 that includes a compressor 10, a combustor 12, and aturbine 13 powered by expanding hot gases produced in the combustor 12for driving an electrical generator 14. Exhaust gases from gas turbine13 are supplied through a conduit 15 to a heat recovery steam generator(HRSG) 16 for recovering waste heat from the exhaust gases. HRSG 16includes high pressure (HP) section 24, intermediate pressure (IP)section 26, and low pressure (LP) section 30. HRSG 16 is configured totransfer progressively lower grade heat from exhaust gases to watercirculating through each progressively lower pressure section. Each ofthe HP, IP, and LP sections 24, 26, and 30 may include an economizer, anevaporator, a superheater and/or feedwater or other pre-heatersassociated with the respective section, such as but not limited to ahigh pressure section pre-heater, which may be split into multiple heatexchangers, which are then positioned in one or more of the sections(HP,IP,LP). The section economizer is typically for pre-heating waterbefore it is converted to steam in for example, the evaporator.

Water is fed to the HRSG 16 through conduit 21 to generate steam. Heatrecovered from the exhaust gases supplied to HRSG is transferred towater/steam in the HRSG 16 for producing steam which is supplied throughline 17 to a steam turbine 18 for driving a generator 19. Line 17represents multiple steam lines between the HRSG 16 and steam turbine 18for the steam produced at different pressure levels. Cooled gases fromthe HRSG 16 are discharged into atmosphere via exit duct 31 and a stack(not shown).

In the exemplary embodiment, combined-cycle power plant 5 furtherincludes a water heater assembly 34 positioned as a stand alone deviceseparate from HRSG 16. In an alternative embodiment, water heaterassembly 34 is positioned within HRSG 16. Water and/or steam areextracted from one or more sections of HRSG and channeled to waterheater assembly 34. A flow of fuel heating water 36 is channeled fromwater heater assembly 34 to a fuel heater 38. A flow of fuel 40 isdirected through fuel heater 38 where flow of fuel 40 receives heattransferred from flow of fuel heating water 36. The heated fuel ischanneled to combustor 12. The cooled flow of fuel heating water 36 isdirected to condenser 20.

FIG. 2 is a schematic diagram of water heater assembly 34 (shown inFIG. 1) in accordance with an exemplary embodiment of the presentinvention. In the exemplary embodiment, water heater assembly 34includes a first inlet configured to receive a flow of at least one ofwater and steam from a first heat exchanger 204 such as an economizer inLP section 30. In the exemplary embodiment, water is supplied to heatexchanger 204 from a condensate pump 206 through conduit 21. A conduit208 from an outlet of heat exchanger 204 branches to supply a flow path210 that channels water heated in heat exchanger 204 to heat exchangersupstream from LP section 30. Conduit 208 also branches into a conduit212 that channels water from heat exchanger 204 to inlet 202. From inlet202 the flow path branches to supply water to a heat exchanger 214 in IPsection 26 through a conduit 216 and a flow control valve 218. Flowcontrol valve 218 is used to control an amount of flow directed to heatexchanger 214, which controls an amount of heat transferred from heatexchanger 214 to the flow of water. IP section 26 may include other heatexchangers and preheaters positioned upstream, downstream, and/orevenstream with respect to a flow in HRSG 16. The flow of water enteringinlet 202 also branches through a conduit 220 to a suction 222 of abooster pump 224. Booster pump 224 provides sufficient head to pump thewater through a flash tank mixing vessel 226 to an outlet 228 of waterheater assembly 34.

Water heater assembly 34 includes a second flow path 230 into flash tankmixing vessel 226 from heat exchanger 214 through a control valve 231and a third flow path 232 from a heat exchanger 234 positioned within HPsection 24 through a control valve 236. In the exemplary embodiment,only three flow paths are illustrated, however in other embodiments moreor less HRSG heat exchangers may be used, which would provide for moreor less flow paths into flash tank mixing vessel 226 from heatexchangers in HRSG 16. Additionally, multiple heat exchanger sectionsmay be coupled in flow communication in parallel, series, orcombinations thereof to provide a predetermined amount of heat from eachsection to flash tank mixing vessel 226. Control valves 218, 230, and236 may be used to modify the heat contribution from each section ofHRSG 16 and from various heat exchangers positioned within thosesections based on a load of the gas turbine engine 13.

During operation, condensate water is heated through low pressureeconomizer 204. A portion of the flow through low pressure economizer204 is channeled to upstream heat exchangers, such as but not limited toa superheater, evaporator, and/or preheaters from other HRSG sections.The remainder of the flow from low pressure economizer 204 is channeledto pump 224 and to flash tank mixing vessel 226 or through control valve218 to heat exchanger 214. The flow through heat exchanger 214 receivesadditional higher grade heat from exhaust gas in IP section 26. The flowthrough heat exchanger 214 is controlled, in the exemplary embodiment,using control valve 231. The flow through heat exchanger 214 ischanneled to another inlet of flash tank mixing vessel 226. A flow offeedwater is channeled through heat exchanger 234 positioned in HPsection of HRSG 16, control valve 236 and into flash tank mixing vessel226 through a third inlet. As used herein, flash tank mixing vesselrefers to a vessel configured to receive flows of fluid at differentgrades of heat and combine the flows such that a flow from an outlet ofthe flash tank mixing vessel is at a temperature and pressure resultingfrom combining and mixing the received flows. Accordingly, in theexemplary embodiment, system 5 includes a controller 240 configured tocontrol the outlet temperature and pressure of the flash tank mixingvessel using any combination of the inlet flows and may control tooutlet temperature and pressure based on a mode of operation of system5. As used herein, a mode of operation refers to a particular equipmentlineup and/or power level output of gas turbine engine 13 and/or steamturbine 18. In the exemplary embodiment, controller 240 includes aprocessor 242 that is programmable to include instructions forperforming the actions described herein. In one embodiment, controller240 is a stand alone controller. In an alternative embodiment,controller 240 is a subpart or module of a larger controller system suchas for example, but not limited to a distributed control system (DCS).

The term processor, as used herein, refers to central processing units,microprocessors, microcontrollers, reduced instruction set circuits(RISC), application specific integrated circuits (ASIC), logic circuits,and any other circuit or processor capable of executing the functionsdescribed herein.

As used herein, the terms “software” and “firmware” are interchangeable,and include any computer program stored in memory for execution byprocessor 242, including RAM memory, ROM memory, EPROM memory, EEPROMmemory, and non-volatile RAM (NVRAM) memory. The above memory types areexemplary only, and are thus not limiting as to the types of memoryusable for storage of a computer program.

As will be appreciated based on the foregoing specification, theabove-described embodiments of the disclosure may be implemented usingcomputer programming or engineering techniques including computersoftware, firmware, hardware or any combination or subset thereof,wherein the technical effect is controlling an amount of heattransferred between a multi stage heat exchanger and a flow of fuel. Anysuch resulting program, having computer-readable code means, may beembodied or provided within one or more computer-readable media, therebymaking a computer program product, i.e., an article of manufacture,according to the discussed embodiments of the disclosure. The computerreadable media may be, for example, but is not limited to, a fixed(hard) drive, diskette, optical disk, magnetic tape, semiconductormemory such as read-only memory (ROM), and/or any transmitting/receivingmedium such as the Internet or other communication network or link. Thearticle of manufacture containing the computer code may be made and/orused by executing the code directly from one medium, by copying the codefrom one medium to another medium, or by transmitting the code over anetwork.

The above-described embodiments of a system and assemblies for heating aflow of fuel provides a cost-effective and reliable means of improvingthe efficiency of the power generation system using water heated usingprogressively higher grade heat from a multi-stage heat exchanger. Morespecifically, the system and assemblies described herein facilitateimproving the efficiency of the power plant by preheating the incomingfuel to a preset temperature. In addition, the above-described systemand assemblies facilitate increasing the fuel inlet temperature to thegas turbine combustor such that the amount of fuel required from thecombustion process to attain the required combustion temperature isreduced thereby improving the overall efficiency of the power generationcycle. As a result, the system and assemblies described hereinfacilitate increasing the efficiency of the power generation system in acost-effective and reliable manner.

An exemplary system and assemblies for heating a flow of fuel usingwater heated using progressively higher grade heat from a multi-stageheat exchanger are described above in detail. The systems illustratedare not limited to the specific embodiments described herein, butrather, components of each may be utilized independently and separatelyfrom other components described herein. Each system component can alsobe used in combination with other system components.

While the disclosure has been described in terms of various specificembodiments, it will be recognized that the disclosure can be practicedwith modification within the spirit and scope of the claims.

1. A fuel supply system comprising: a water heater assembly configuredto heat a flow of water by mixing progressively higher grade heatedflows of at least one of steam and water from a multi-stage heatexchanger arrangement; a fuel inlet flow path configured to receive aflow of fuel; and a fuel heater comprising a first flow path coupled inflow communication with said fuel inlet flow path, said fuel heatercomprising a second flow path coupled in flow communication with saidwater heater assembly, said fuel heater configured to transfer heat fromthe flow of water to the flow of fuel.
 2. A system in accordance withclaim 1 wherein said water heater assembly is configured to receive aflow of condensate water from a relatively lower pressure heat exchangerpositioned in the multi-stage heat exchanger arrangement.
 3. A system inaccordance with claim 2 wherein said water heater assembly comprises afirst flow path wherein the received flow of condensate water ischanneled through a relatively lower pressure heat exchanger positionedwithin the multi-stage heat exchanger arrangement to a flash tank mixingvessel using a pump.
 4. A system in accordance with claim 2 wherein saidwater heater assembly comprises a second flow path wherein the receivedflow of condensate water is channeled through a relatively intermediatepressure heat exchanger positioned within the multi-stage heat exchangerarrangement to a flash tank mixing vessel.
 5. A system in accordancewith claim 4 wherein a temperature of the flow of fuel is controlledusing an inlet flow to said intermediate pressure heat exchanger.
 6. Asystem in accordance with claim 1 wherein said water heater assembly isconfigured to receive a flow of feedwater from a relatively highpressure heat exchanger positioned within the multi-stage heat exchangerarrangement, said water heater assembly comprising a third flow pathfrom the high pressure heat exchanger to the flash tank mixing vessel.7. A system in accordance with claim 1 wherein said multi-stage heatexchanger arrangement comprises an intermediate pressure section thatincludes an intermediate pressure heat exchanger positioned downstreamof at least one of an intermediate pressure evaporator and anintermediate pressure superheater in a direction of a gas flowpaththrough the multi-stage heat exchanger arrangement.
 8. A system inaccordance with claim 1 wherein said multi-stage heat exchangerarrangement comprises a high pressure section that includes a highpressure heat exchanger positioned downstream of at least one of a highpressure evaporator and a high pressure superheater in a direction of agas flowpath through the multi-stage heat exchanger arrangement.
 9. Asystem in accordance with claim 1 wherein said multi-stage heatexchanger arrangement comprises a low pressure section that includes alow pressure heat exchanger positioned downstream of at least one of alow pressure evaporator and a low pressure superheater in a direction ofa gas flowpath through the multi-stage heat exchanger arrangement.
 10. Asystem in accordance with claim 1 wherein said multi-stage heatexchanger arrangement comprises an intermediate pressure section thatincludes a high or intermediate pressure heat exchanger positionedadjacent to an intermediate pressure heat exchanger and downstream of atleast one of an intermediate pressure evaporator and an intermediatepressure superheater in a direction of a gas flowpath through themulti-stage heat exchanger arrangement.
 11. A system in accordance withclaim 1 wherein said multi-stage heat exchanger arrangement comprises ahigh pressure section that includes an intermediate pressure heatexchanger positioned adjacent to a high pressure heat exchanger anddownstream of at least one of a high pressure evaporator and a highpressure superheater in a direction of a gas flowpath through themulti-stage heat exchanger arrangement.
 12. A system in accordance withclaim 1 wherein said multi-stage heat exchanger arrangement comprises alow pressure section that includes an intermediate or high pressure heatexchanger positioned adjacent to a low pressure heat exchanger anddownstream of at least one of a low pressure evaporator and a lowpressure superheater in a direction of a gas flowpath through themulti-stage heat exchanger arrangement.
 13. A system in accordance withclaim 1 wherein said water heater assembly comprises a pump configuredto boost the pressure of the flow of water through a flash tank mixingvessel in said water heater assembly and said second flow path of saidfuel heater.
 14. A water heater assembly configured to heat a flow ofwater by mixing progressively higher grade heated flows of at least oneof steam and water from a multi-stage heat exchanger arrangement, saidwater heater assembly comprising: an inlet configured to receive a flowof condensate water from a relatively lower pressure heat exchangerpositioned in the multi-stage heat exchanger arrangement; and a flashtank mixing vessel comprising a plurality of inlet flow paths and anoutlet, said flash tank mixing vessel configured to receive a flow of atleast one of steam and water from a respective heat exchanger in themulti-stage heat exchanger arrangement coupled in flow communication toeach of the plurality of inlet flow paths.
 15. An assembly in accordancewith claim 14 wherein a temperature of the flow of condensate water atthe outlet is controlled using an inlet flow to at least one of saidrespective heat exchangers.
 16. An assembly in accordance with claim 14wherein said multi-stage heat exchanger arrangement comprises anintermediate pressure section that includes an intermediate pressureheat exchanger positioned downstream of at least one of an intermediatepressure evaporator and an intermediate pressure superheater in adirection of a gas flowpath through the multi-stage heat exchangerarrangement.
 17. An assembly in accordance with claim 14 wherein saidwater heater assembly further comprising a pump configured to boost thepressure of the flow of water through said water heater assembly to awater heater assembly outlet.
 18. A fuel heater assembly configured toheat a flow of water by mixing progressively higher grade heated flowsof at least one of steam and water from a multi-stage heat exchangerarrangement, said fuel heater assembly comprising: a water heaterassembly comprising: a plurality of inlet flow paths configured toreceive a flow of at least one of water and steam from respective heatexchangers positioned in the multi-stage heat exchanger arrangement, therespective heat exchangers corresponding to a plurality of differentgrades of heat in the multi-stage heat exchanger arrangement; and anoutlet configured to channel the heated flow of condensate from thewater heater assembly; and a fuel heater comprising a first flow pathconfigured to be coupled in flow communication with a flow of fuel, saidfuel heater comprising a second flow path configured to be coupled inflow communication with said outlet, said fuel heater configured totransfer heat from the flow of water to the flow of fuel.
 19. A fuelheater assembly in accordance with claim 18 wherein said multi-stageheat exchanger arrangement comprises an intermediate pressure sectionthat includes an intermediate pressure heat exchanger positioneddownstream of an intermediate pressure superheater in a direction of agas flowpath through the multi-stage heat exchanger arrangement.
 20. Afuel heater assembly in accordance with claim 18 wherein saidmulti-stage heat exchanger arrangement comprises an intermediatepressure section that includes a high or intermediate pressure heatexchanger positioned adjacent to an intermediate pressure heat exchangerand downstream of an intermediate pressure superheater and anintermediate pressure evaporator in a direction of a gas flowpaththrough the multi-stage heat exchanger arrangement.